Osmotic dispensing systems for delivering various useful agents to an environment of use are known to the prior art in U.S. Pat. No. 3,845,770 issued to patentee Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899, issued to the same patentees. The osmotic systems disclosed in these patents are manufactured in the form of osmotic dispensing devices and they comprise a semipermeable wall surrounding a compartment that contains an agent. The wall is permeable to the passage of an external fluid, and it is substantially impermeable to the passage of agent. The osmotic systems have a passageway through the wall that connects the compartment with the exterior of the device for delivering the agent from the device. These devices deliver an agent by imbibing fluid through the wall into the compartment, at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall, to produce an aqueous solution containing agent that is delivered through the passageway from the device. The devices are effective for delivering, (a) an agent that is soluble in fluid imbibed into the compartment, thereby forming a solution of the agent that is delivered from the device, and also for delivering, (b) an agent that is poorly soluble in fluid and is mixed with an osmotically effective solute that is soluble in fluid imbibed into the device, thereby forming a solution of the solute containing agent in suspension that is delivered from the device.
Osmotic devices having composite walls are described in U.S. Pat. No. 4,077,407, issued to Theeuwes and Ayer. This patent describes osmotic devices having walls formed of a first polymer stabilized with a second polymer, and optionally the wall can contain a dispersant, a plasticizer, or a flux enhancer. The composite wall of these devices are coated from organic solvents. The walls are made as composites for increasing their resistance to hydrolysis in the presence of agents over a wide pH range, for increasing their exclusion towards agents, and for increasing their flux rates.
The prior art osmotic devices described above represent an outstanding advancement in the drug delivery art, and they are useful for delivering innumerable beneficial agents to many environments of use. It will be appreciated by those versed in the delivery art, that improvements can be made in the wall, the usefulness of the devices can be increased, and consequently their applications broadened, if devices are provided having walls possessing desirable permeabilities and formed of biologically acceptable materials applied from nontoxic solvent systems. For example, both the wall and the usefulness of a device would be unexpectedly increased, if (a) an osmotic device is provided with a pharmaceutically acceptable wall comprising a cellulose ether formulation possessing permeability characteristics conducive for delivering agents to biological environments and if, (b) the wall is formed with nontoxic solvent systems that are non-deleterious and innocuous to the biological environment and the atmosphere, and (c) the wall-forming material is particularly resistant to physical or chemical change in the presence of these agents.